This addresses an objective of central importance in current biophysics-namely to determine those structural and dynamic features of phospholipid molecules that control the distribution and function of membrane-bound enzymes. This objective will be determined through three specific aims: 1) To determine whether membrane proteins partition into regions of particular chemical structure or physical order in complex lipid environments, and to determine how the above partitioning characteristics affect the function of membrane- bound enzymes. The protein to be used is CaATPase from rabbit skeletal muscle. 2) To determine the conformational changes that occur in both the lipid and protein components upon their mutal interaction in model vesicle systems and in a reasonable simple native tissue (lung surfactant) to be studied in vitro. 3) To determine the orientation of peptides inserted into lipid bilayers in a film composed of oriented arrays of lipids. The physical methods to be used to address the specific aims are Raman and FT-IR spectroscopies and Differential Scanning Calorimetry. Purified CaATPase will be reconstituted into binary lipid mixtures selected to mimic the phase properties of native membranes and to be amenable to detailed spectroscopic analysis. Parallel enzyme activity and physical measurements will be used to achieve Aim 1. The essential components of lung surfactant will be studied individually and in combination to achieve Aim 2. ATR techniques will be used to address Aim 3.